BMI: A Tool for Confusion and Politics

January 19, 2013

The U.S. is obese. That is the message from government and so-called
health experts. There is no way around it, they say. And the only way to
get un-obese is to do what they say. But are we really obese? Or are the
alleged experts wrong?

First things, first, what is BMI? BMI is an initialism for “Body Mass
Index”. Put simply it is a ratio. It is your weight compared to your
height. That is all it is. It does not measure your health, it does not
measure your fitness, it does not tell you if you are fat or not. If you
want more details on it, see the Wikipedia entry.

So, if it does not measure if you are fat or not, why are we judged
fat-or-not based on it? Laziness. Maybe Laziness and confusion. Those
who push nutritional guidelines or worse, government mandates, based on
BMI presumably have good health in mind. However, if health is as
important as they say, why skimp on the data? Why use a proxy of a proxy
of a proxy for approximate data to base conclusions and recommendations
on? Put simply, because it is easy.

The fundamental problem is the notion we can distill healthiness to a
single number. Yet, two people with identical BMIs can vary tremendously
in their appearance, body fat percentage, and health. Because of this,
BMI is a terrible choice to distill it down to.

Jason Seib has an excellent article illustrating this in a visual way
you can not argue with. While the article “Attention Scale Addicts,
p2” discusses it in the context of trusting the number on the scale
it is also a clear description of the problem with BMI. Consider the
image in the article:

Same BMI, same result?

The woman in the picture, Deb, started at 155 pounds. She ended at the
same weight. Yet clearly, if we were to pick a visual example of which
one looks healthier we would choose the right side. To see her in action
check out some Youtube videos where she lifts and exercises.

More good examples of why BMI is bad can be seen at Julianne’s Paleo
& Zone Nutrition site. She has en excellent summary of key
measurements of Deb Hunter summarized so I won’t repeat them here. She
also links another article with the following pictures:

I think we can agree the heavier weight does not make her look fat.

Same BMI, Same Person, Not the 'same body'

There is a good reason both of these pictures tell us why BMI is bad.
Muscle is more dense than fat, so it takes more muscle to get the same
size than fat. To put it another way, three pounds of muscle takes up
the same space as one pound of fat.

So if BMI isn’t an indicator of being fat or obese, should we use it?
No. And in my opinion the moment your doctor starts talking about your
BMI it is time to find a new one. Instead he should be talking to you
about your level of inflammation, your body fat percentage, and what
actually ails you.

Before I leave you to ponder why people who assert they are just trying
to get us all to be healthier, I’ll post a nice extreme example. We all
like them, but it also helps to show the above photos and people are not
freaks the BMI just doesn’t account for, but are regular people.

Now, I’m not saying next photo is of a freak, but his BMI as calculated
by his public stats as of the time I write this indicates he is
“overweight” and close to being “obese”.

Obese? Oh yeah, totally.

Yes, most of us (self included) could and should be healthier and more
fit. We do need work. What we don’t need is an emphasis on changing a
meaningless number.